A recent study concluded that regular physical exercise has a greater effect on cognitive abilities than the previous estimation and moderate exercise can directly improve brain functioning even in old age.

A) the previous estimation and moderate exercise
B) previous estimation and that exercising moderately
C) estimated previously and moderate exercise
D) estimated previously and that moderate exercise
E) previously estimated and that exercising moderately

A recent study concluded that regular physical exercise has a greater effect on cognitive abilities than the previous estimation and moderate exercise can directly improve brain functioning even in old age.

A) the previous estimation and [that]moderate exercise
"That" is missing to signify proper parallelism. This puts "previous estimation" and "moderate exercise" as parallel items, which is not the objective of this sentence

B) previous estimation and that exercising moderately
"exercising moderately" is not parallel to "regular physical exercise"

C) estimated previously and [that] moderate exercise
As in Option A "That" is missing to signify proper parallelism.

D) estimated previously and that moderate exercise
Correct answer for maintaining parallelism

E) previously estimated and that exercising moderately
"exercising moderately" is not parallel to "regular physical exercise"